NASA has issued a new Request For Information (RFI) that shows there is a deadline for the Space Launch System (SLS) to transition to “Advanced (Evolved) Boosters” no later than the ninth flight. This is due to a future obsolescence issue with the current booster design which relies on Shuttle heritage components of which there is only a limited amount of stock remaining. NASA intends to purchase another six SLS flight booster sets before the stock runs out, prior to moving to the Advanced Boosters.The Space Launch System includes a mix of former Shuttle and Constellation (CxP) hardware, a winning design from numerous studies conducted by the Marshall Space Flight Center (MSFC) via political guidance provided in the 2010 Authorization Act.

The motor is now classed as qualified allowing for the production of the first flight booster set for Exploration Mission -1 (EM-1). Production has already started on the booster set for the second mission.

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NASA has already contracted Orbital ATK for the first three booster sets, along with “Flight Support Booster-One (FSB-1)” as a back up to the flight boosters.

NASA’s latest Request For Information (RFI) is a government acquisition requirement where companies can bid and then win future contracts with NASA, although as with most SLS contracts only one company is in the running.

That becomes more obvious for the first element of the document, which notes NASA will purchase six more sets of five segment boosters. Only Orbital ATK will be able to produce the baselined boosters that will ride with the Block 1 and initial Block 1B SLS launches.

“The Boosters remain the same in both Block 1 and Block 1B and are based on Shuttle heritage with many components preserved from the Shuttle program.”

Such components include the casings that house the propellant in each segment. Most of the casings were reused from previous Shuttle missions, with the boosters parachuting to the Atlantic Ocean before being recovered and towed back to Port Canaveral.

Other obsolescence items listed are less specific but include “material suppliers; major structures; thrust vector control; motor cases; propellant, liner, and insulation; and nozzle ablative liners and metal housings.”

SLS does not intend to recover the boosters, a by-product of the Constellation Program (CxP) which suffered from performance issues, in part resulting in the deletion of the parachute and recovery systems on the boosters. Despite SLS’ superior performance, the chutes were not brought back into the design, as such they will fire for the first two minutes of first stage flight, separate and then crash into the Atlantic before sinking to the ocean floor.

This ultimately means the loss of hardware that would normally be fed back into the production line. With no plans to restart production, NASA has opted to use up the remaining stock and use it as a catalyst to bring the Advanced – also cited as “Evolved” in some documentation – Boosters online.

An EM-1 Booster Segment in production – Orbital ATK

“Eventually NASA will run out of the heritage Shuttle components and a replacement design is needed to address this future obsolescence,” added the RFI.

“That replacement design will be included in the Block 2 version of the SLS. It is expected that the replacement design will provide the same or higher ascent performance than the existing heritage design,” the overview noted, confirming this document was citing the Advanced Boosters as the replacement. “How much extra performance is possible in a replacement design is of significant interest to the government.”

Nearly six years ago, Dynetics, Inc. and Pratt & Whitney Rocketdyne (PWR) formed a team “to offer an affordable booster approach that meets the evolved capabilities of the SLS” – and presented their overview at the 63rd International Astronautical Congress, Naples, Italy in 2012.

However, the document leaves the door open for a second round of evolving the concepts past the original proposals for the Advanced Boosters.

Orbital ATK’s original proposal for Advanced Boosters

Due to the aforementioned lack of Shuttle heritage stock for the current boosters, moving to the Advanced Booster must now become a reality by the ninth flight of SLS.

“The intent of this acquisition is to extend the life of the current Booster design through the available Shuttle heritage inventory while developing replacement designs to be ready when that inventory runs out,” noted the RFI.

“Because approximately eight flight sets of heritage hardware were preserved at the end of Shuttle, a new Booster for Block 2 must be developed, certified, and produced on or before the ninth flight of the SLS.”